Concrete mixer



Dec. 15, 1953 C.'GERST v 2,

' CONCRETE MIXER (iris 66/152? INVENTOR. L

Dec. 15, 1953 c. 'GERST 2,662,755

CONCRETE MIXER Filed Dec. 11, 1951 3 Sheets-Sheet 2 b A44 Vii/7'5 62/122,

C. GERST CONCRETE MIXER Dec. 15, 1953 5 Sheets-Sheet 3 Filed Dec. 11, 1951 a y a 1 M Z W 0 a 1 fi fi 4 v a a M w v 5 a w Patented Dec. 15, 1953 CONCRETE MIXER Chris Gerst, Detroit,- Mich., "as'sigiioi', Qb'y inesfne assignments, to Le Roi compan Mil'vtaillie, Wi's., a corporationof Wisconsin Application December 11, 1951, 'Serial'No. 261,100

18 Claims.

This invention relates to concrete mixers and has particular reference to the material charging and discharging provisions for transit mixers of the end loading and discharging type.

In mixers of this type the charging device or hopper is provided with QlOti'i-tdblE-jillOStl-TG for sealing against the charging and discharging opening in the end of the mixing drum. Considerable difiiculty has been experienced heretofore in connection with the bearing between such rotatable closure and the hopper due principally to the fact. that wet or dry gets into the bearing and quickly destroys the same. Numerous seal arrangements have been suggested to overcome this difficulty butthey have-not proven to be satisfactory in that they fail to exclude abrasive material-from the bearing, with the result that the bearing has a relatively short life.

According to my invention the hopper, the -r tatable closure carried thereby, and the bearing are constructed and arranged insuch'a manner as to prevent the mix, either wet or from getting into the bearing, with the result that the life of the bearing is substantially prolonged,

In accordance with my invention. the bearing means between the hopper andtheclosure is constructed so that one of the joints of said bearing is exposed to the interior; of the hopper; the other of the joints of the bearing isv exposedtotheoutside of the hopper andthe closure; and a labyrinth effect is, provided: between the bearing surfaces and the joint exposed to them-- terior of the hopper: so as to exclude abrasive materialfrom the bearing surfaces, the location of such joint so that it is exposed to the interior of the hopper further. preventing. wet mix from getting into the bearing.

A principal object of the invention. therefore, 7

is to provide a new and improved" charging-- and closure device for concrete mixers.

Another object of the invention is toprovide a new and improved bearing construction for devices of this kind.

Other and further objects of the inventionwill be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are three sheets, which by way of illustration show preferred-embodiments of the invention and-what I now consider to be the best mode in" which 1': have contemplated applying the principles of my invention.- Other embodiments of the: invention maybe used without departing fromthescope of the present, inventionas set forthin the ap-- pended claims.

Fig. 1 is an end savanna new oi a taste mit e o ne inventi01i;.. Fig. 2 is an enlarged-fragmentary elevational view of the closure device;

the drawings:

Fig. 3;i s an enlarged fragmentary sectional view talgen-along the line;3-3 of Fig. 2;

Fig. 4 is a fragmentarysectionalview taken along the'line 4-'4 ofjigZ;

Fig. 5 is a fragmentary sectional viewta ken on th e 'q 1.F Fig. 6 is a fragmentary ection'al view similar to Fig. 3;, showing a modification of the invener: nd Figs. '7, 8 and 9 are sectional views similar File. a butshow-ing modified minis or tearin structures between the hopper and the closure carried thereby I I I As illustrated in Figs. 1 to 5 inclusivea crete mixer embodying my invention in general a rotatable mixing trum et prof/i with an opening 22 at one end thereof gh which material is charged into and discharged from the drumr An amnion closure 24 1s eh;- gageable with the drum "26 around the periphery of-the opening 22 and is rotatable with th'e drum when soengaged as'sho'wn iii-Fig. 3. Theo 24 'is' movable from the 26 so as to permit the discharge or; material from the drum through the ope'nin Amaterial receivin s ii .w'h l' i 'i closure 24 is rotatably mounted steepness charge material through the opening the closure 24 and into the drum through the open: ing- 22 thereof whenthe closure is sealing the opening 22 in the drum, as shown in Fig. 3; The closure and hopper are supportedformovement away: from and toward the drumsoasto permit discharging of the drum wh'enthe closure 24' is away from the opening 2 2-, and to permit charging of the: drumwhen the closure -21l,-is seating-against: the end' of the drum and closing the'opening 22, as shown in- Fig. 3.

Bea-ring means indicated generally at are provided between the closure 2% and the hopper 2 6 toipermit relative rotation therebetweenwhen the closureis rotating with the drum; such hearing means being constructed so that one of the joints 30 thereof is" exposed to the interior of the hopper and the other of the joints :32-therepertains, the interior of the drum is provided with a series of axially and/or spirally extending blades 34 which during rotation of the drum 20 in one direction feed the material axially away from the opening 22 and serve to mix such material, and upon rotation of the drum 20 in the other direction about its axis serve to effect the discharge of the mixed material from the drum through the opening 22 thereof, the closure 24 at such time being away from the end of the drum 2050 as to expose the opening 22.

The drum 20 is journalled for rotation about its longitudinal axis and may be driven, for example, by the drive arrangement as shown in Gerst Patent No. 2,556,034, issued June 5, 1951.

As shown in Fig. 1, a pair of rollers 36 rotatably support the open end of the mixing drum 20 which is provided with a ring 38 which runs on the rollers 36 and thereby rotatably supports the open end of the mixing drum. The hopper 26 is provided with two arms or brackets 40, the outwardly projecting extremities 42 of which are mounted on arms 44 of a cross frame 46. The frame 46 is provided with two laterally extending tubular supports 48, each of which is supported by a series of rollers 56 carried by extensions 52 of the mixer frame, there being a series of rollers 50 on the extensions 52 both above and below the supports 48 so that the frame 46 is supported for movement in a horizontal direction and so that the closure 24 carried by the hopper 26 will move away from and toward the drum.

Actually, the supporting arrangement just described supports the closure 24 for movement along the axis of the drum 28 and with the axis of rotation of the closure 24 coinciding with the axis of rotation of the drum 20.

A hand wheel 54 connected to gearing 56 is arranged to operate a rock shaft 58 journalled in bearing 68 on the frame, the shaft 58 being provided with arms 62 which in turn are connected to links 64 carried by the frame 46 so that upon turning of the rock shaft 58 in one direction, the closure 24 and the hopper 26 will be moved away from the end of the drum 20 so as to expose the opening 22 thereof in order to permit discharging of the drums contents, while upon rotation of the rock shaft 58 in the other direction the closure 24 will be moved so as to seat against the end of the drum and thereby seal the opening therein and thus position the hopper 26 so that material fed into the hopper will be charged into the drum 20 through the opening 22.

An adjustable link 65 connected to the hopper 26 and the frame 46 adjustably secures the hopper 26 relative to the frame 46 so that the plane of the closure 24 will be parallel with that of the end of the mixing drum 20. The mixer is also provided with chutes 66 positioned adjacent the opening 22 so as to direct material discharged therefrom into a discharge chute 68 adjustably mounted on the back of the mixer frame. The mounting of the chute 68 is disclosed and claimed in my copending application, Serial No. 257,486 filed November 21, 1951, now Patent No. 2,646,262, dated July 21, 1953, for Discharge Chute Mounting for Concrete Mixers.

As shown in Fig. 3, the closure 24 comprises an annular disc-shaped ring or plate to the inside face I of which a gasket I2 is suitably secured, the gasket I2 being adapted to seat against and form a seal with a metal ring I4 welded or otherwise suitably secured to the end of the drum so as to define the opening 22 therein.

As shown in Figs. 1 to 5, the hopper is provided with a flange 76 which is bolted or otherwise rigidly secured to a sealing ring or annular member 18. A bearing ring or annular bearing member 80 is rigidly secured to the ring I8 by a series of bolts 82, each of the bolts extending through an opening in the ring I8 and being threadedly secured in threaded holes in the bearing member 80. The annular closure 24 has rigidly secured within its central opening an annular bearing ring retainer 84 which is bolted to the closure 24 by a series of bolts 86. The ring or retainer 84 cooperates with a sealing ring 08 to define a cavity or chamber in which the bearing ring 88 is disposed, the ring 88 being rigidly secured to the ring 84 by a series of bolts 80. The inner peripheries of the rings 18 and 88 in addition form a part of the discharge hopper, and the ring 88 has secured thereto a cylindrical member 92 which forms a continuation of the hopper and which extends into the drum 20 beyond the ends of the blades 34 a substantial distance so as to discharge material fed into the hopper 26 into the drum at a distance inwardly away from the opening 22 in the drum. This arrangement not only facilitates charging and substantially reduces the charging time, but in addition the member 92 serves to exclude wet mix from the joint 80 between the rings I8 and 88. The member 92 is rigidly secured, such as by welding, to the ring 86, as shown in Fig. 3, and the interior surface of the member 92 forms a continuation of the hopper.

The rings 78, 80, 84 and 88 are so designed that the bearing surfaces are formed by outer peripheral cylindrical surfaces 94 and 96 of the bearing ring 80, and inner cylindrical surfaces 91 and 93 of the ring 84. In addition, the radially extending surfaces I00 and I02 of the ring 80, I64 of the ring 84, and I60 of the ring 88 form the thrust bearing surfaces of the bearing 28. The rings 18, 88, 80 and 84 are designed so as to provide a labyrinth effect indicated generally at I88 between the joint 30 and such bearing surfaces. In addition, the rings are made so as to provide annular grease pockets or channels H0, H2, H4, H6, H8 and IIS adjacent to the bearing surfaces.

As shown in Fig. 3, the rings I8 and 80 are provided with a duct I20 which communicates,

at one end with the grease pocket H6 and at its other end with a grease fitting I22 secured to the ring "I8, whereby grease may be supplied tothe bearing surfaces 94 and 96, 81 and 98.

As shown in Fig. 5, the rings 18 and 80 are provided with a duct I24 communicating at one end with the grease channel I I4 and at the other end with a grease fitting I26, whereby grease may be supplied to the channel H4 and the adjacent grease channels not only for lubrication purposes but also for the purpose of excluding abrasive material from the bearing surfaces previously referred to.

As shown in Fig. 4, the ring 18 is provided with a duct I28 which communicates at one end with the grease channel I I0 and at the other end with a grease fitting I30, whereby grease may be supplied to the channel I50 and to the joint 30 between the rings 18 and 88 so as to exclude dirt and foreign material from the bearing surfaces. Grease will also be supplied through the arrangement described to the clearances between the labyrinth effect I08 between the rings 78 and 88 so that this also will serve to exclude dirt and other foreign material from the bearing surfaces.

adamant The joint 32, because-it is 'exposed to 'the outside of the closure -24 *and the hopper :26, is {not ex- -pesed' togrit-and dirt as islthe joint-=30.

The parts "18 -and88--are so-designed that the gap therebetween is 'ofthe order of .016 in. *andthis gap is filled with grease from the fitting 130 which functions .to exclude dirtand'material from the bearing. In addition, 'the chute extension 82 functions as abaffle to exclude wet mix from the joint 30.

the closure 24 rotates with the drum '20 when-the closure 24 is in its closed position as shown in Fig. '3, the-bearing 2-8 will be subjected tea-cocking or distortion if there-is any-misalignment between the drum 20 and the closure. Due tc-the size of the parts and the load carried "by the mixer andthe jolting'to which'the mixer is-subjected while in transit, it is'impossible to "always maintain-the closure 24 aligned with the mixing drum 29, with theresult that-the bearing '28 is subjected to considerable loads. It will'be noted that in the bearing construction as disclosed herein the bearing surfaces 94, 96, S l-and {38 are cylindrical surfaces which extend axially ofthe-axis of rotation of the drum for a substantial distance, and :this disposition of the bearmg-surfaces reduces to an appreciable extentthe possibility of rapid wearon the bearing whenever misalignment may occur between the closure 24 and the drum'2'll.

To further reduce the effect of misalignment between the drum 20, the closure 24, and the bearing- 28, the modified arrangement disclosed -in Fig. 6 may be employed wherein the closure -24 instead of being bolted directly to the ring 34, i

cost-of manufacture. In these modifications the same-reference characters are used as previously *used to indicate thesame parts.

As shown in Fig. 7, the bearing is provided by two rings I56 and I52, the ring I'5II'being provided with cylindrical bearing surfaces I54 and IE6, while the ring I52 isprovided with cylindrical bearing surfaces I58 and I60. In addition, thrust bearing surfaces I62 and I64 are provided. The ring I59 is rigidly secured to the closure 24 'bymeans of aseries of bolts I66. Of course, the modification disclosed in Fig. 6 may be used in connection with any of the embodiments of the invention disclosed in this application. The ring 152 is rigidly secured by a series of bolts I68 to the hopper I10 corresponding with the hopper 26. In this case the flange I12 of the hopper I'Til to which the ring I52 is secured is provided by a ring welded to the hopper chute I-"I-Il. Adjacent portions-of the ring I12 .andthe ring I59 define a gap'or joint I14 which is exposed to the-inside of the hopper, like the joint 30. The chute '92 is weldedto the ring I and extends into the drum aSfS'i'lOWlfl in Fig.3. The rings I50 and I52 are provided with annular channels or grease pockets :xIilLB and IE8 which are supplied with grease lthrough grease -fittings I80 so that the bearing surfaces will'belubricated andso that the grease ihopper.3fl.8 and .the closure 24.

pocket :ILH; "will be rdisposedibetween'itheidearing surfaces and the joint 1:14. :Thexinterfltting ear- ;rangement .of the shoulders :on thezrings I250 ean'd I52 adjacent :the grease spocket A18 gPIZOVidBS :a labyrinth efiect.shetween'rtheijoint :.I M anti-.the bearing surfaces. 1

In :theamodification shown in .liig. :'8,-.a chanmeleshapedming 1-200 :is secured tothe .61051116 -24 by "a series -;:of :bolts 20.2. .The Zbearing ring 2M iis'tboltedtofthetfiange 20$ ui'f thethopper'208 .hyz'a series 'of bolts 2 m. in this :case the "hopper 10B is ;provided with ':a :lip 2| 2 {which I overhangs tone edge '2 HI of the ;m'ng.:200 -and definesza joint 2.1 B ztherebetween. Therings 20Il:and 204,.alon-gwith the-lip 2L2, providea labyrinth effect .2 I8 between the joint 2 I6 and theabearingrsurfaces 220 ands22-2. .addition therrings 2.00 :and .204 are'formed .to 'provideya :seriesof grease pocketszor grease channels 224,. 226,228 :and 230 which maybe supplied with grease through; grease fittings in a manner :similartothat shown in the previous modifications. In the casezoi. :Fig. 8, the-thrust bearing surfaces 232 and 234 are also provided.

In .the modification shown in :Fig. 19 the :ring JINLis secured to the :closure 24 by 'a'series of iboltsz3'fl2, while the ring 30,4 isrigidlysecured gtothe flange 3.06 of thehopper 1 308 by a series-of bolts 3-). The rings .300 and 304 are provided with .interengageable cylindrical bearingzsurfaces 3 I2, 3 I4 and 3 I I5 and thrustibearing surfaces. 18, 320,322 and 324'. Airing 1325 :is b.oltedto'=.one.-face of Ithe:.ring 1300 by a series OfbOLtS such as :Allen head screws 32-8 before the ring t3-M#isiboltcd t0 the flange 306, and this ring-326 :withthe ring which forms the flange'306 'of '.the.-hopper'forms one of the joints 13.30 i of the bearing :between the Th j n 30. like the joints 2 I6 and 114- of theprev-ious modifications, isa gap of thezsame sizeas that'of the joint 30 and, like the joints 130., I14 and 2H5, is filled with grease vfor the ,purpose of nexcluding dirt from the bearing surfaces.

.Forthe purpose of supp1ying grease tothe, joint 330 and grease'toxthe grease channelsor pockets 332 r and :3, ;lubricati0n provisions -.of the type :shown .in Figs. 3 to? may be employed. The grease suppliedto ithe joints exposed to' the interior of the-hopper in all of :the modifications :shown in thisapplication, as wellas tothe other joints of the hearing which are exposed to the outside of the closureand the hopper, lnotaonly :serves for lubrication, purposesbutalso to exclude dirtand abrasivematerial from the bearingsurfaces. It is desirable thatithese .ioints be well supplied with grease and .frequently lubricated so as to flush out of thejointsany dirt onforeisn material which may contaminate the .grease therein.

It will be observed in all of themodifications illustrated ithat the bearing surfaces comprise en- .gageable cylindrical surfaces of substantial axial extent which are :protected by grease channels and alabyrinthzeffect from :theonejoint which isexposed-to the interiorof the hopper, andithat in all of the modifications :shown the other 0f thejoints between the hopper and the closure is exposed to the outside of the hopperand the closure. .It will also be noted that each of the'bearingsincludes thrust bearing surfaces for taking the axial thrustbetween the closure-and the hopper and that these thrust "bearing surfaces are likewise protected from the joint of the bearing which is exposed to the interior vof the hopper.

'While I have illustrated and described prefferred emhodiments'of. my invention, it.'is under- I stood that these are capable of modification and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a concrete mixer having a rotatable mixing drum provided with an opening through which material is charged into and discharged from said drum, a closure engageable with said drum for sealing said opening and being rotatable with said drum when so engaged, said closure being movable away from said drum so as to permit the discharge of material therefrom through said opening, a material receiving hopper provided with a chute extending through said closure and into said drum through said opening when said closure is sealing said opening, said chute comprising a member carried by said closure and extending into said drum a substantial distance so as to charge material fed into said hopper into said drum at a distance inwardly away from said opening in said drum, means supporting said closure and hopper for movement away from and toward said drum, and means providing a bearing between said closure and hopper to permit relative rotation therebetween when said closure is rotating with said drum.

2. Apparatus according to claim 1 wherein said bearing means is constructed so that one of the joints thereof is exposed to the interior of said hopper and the other of the joints thereof is exposed to the outside of said hopper and closure.

3. In a concrete mixer having a rotatable mlxing drum provided with an opening through which material is charged into and discharged from said drum, a closure engageable with said drum for sealing said opening and being rotatable with said drum when so engaged, said closure being movable away from said drum so as to permit the discharge of material therefrom through said opening, a material receiving hopper extending through said closure for charging material into said drum through said opening when said closure is sealing said opening, means I.

supporting said closure and hopper for movement away from and toward said drum, and means providing a bearing between said closure and hopper to permit relative rotation therebetween when said closure is rotating with said drum,

said bearing means comprising a ring fixed to said closure member for rotation therewith, a ring fixed to said hopper, said rings having interengageable annular axially extending bearing surfaces concentric with the axis of rotation of said drum, said rings being constructed and arranged and so secured to said closure member and hopper that one of the joints between said rings is exposed to the outside of said closure and hopper and the other of said joints is exposed to the interior of said hopper, said rings being constructed to provide a labyrinth effect providing a seal between said other of said joints and said bearing surfaces and a grease channel adjacent to said bearing surfaces.

4. In a concrete mixer having a rotatable mixing drum provided with an opening through which material is charged into and discharged from said drum, a closure engageable with said drum for sealing said opening and being rotatable with said drum when so engaged, said closure being movable away from said drum so as to permit the discharge of material therefrom through said opening, a material receiving hopper provided with a chute extending through said closure and into said drum through said opening when said closure is sealing said opening, said chute comprising a member carried by said closure and extending into said drum a substantial distance so as to discharge material fed into said hopper into said drum at a distance inwardly away from said opening in said drum, means supporting said closure and hopper for movement away from and toward said drum, and means providing a, bearing between said closure and hopper to permit relative rotation therebetween when said closure is rotating with said drum, said bearing means comprising a ring fixed to said closure member for rotation therewith, a ring fixed to said hopper, said rings having interengageable annular axially extending bearing surfaces concentric with the axis of rotation of said drum, said rings being constructed and arranged and so secured to said closure member and hopper that one of the joints between said rings is exposed to the outside of said closure and hopper and the other of said joints is exposed to the interior of said hopper.

5. Apparatus according to claim 4 wherein said rings are constructed to provide a labyrinth elfect between said other of said joints and said bearing surfaces and wherein a grease channel is provided adjacent to said bearing surfaces.

6. In a concrete mixer having a rotatable mixing drum provided with an opening through which material is charged into and discharged from said drum, a closure engageable with said drum for sealing said opening and being rotatable with said drum when so engaged, said closure being movable away from said drum so as to permit the discharge of material therefrom through said opening, a material receiving hopper provided with a chute extending through said closure and into said drum through said opening when said closure is sealing said opening, said chute extending into said drum a substantial distance so as to charge material fed into said hopper into said drum at a distance inwardly away from said opening in said drum, means supporting said closure and hopper for movement away from and toward said drum, and means providing a bearing between said closure and hopper to permit relative rotation therebetween when said closure is rotating with said drum, said bearing means comprising a ring fixed to closure member for rotation therewith, a ring fixed to said hopper, said rings having interengageable annular axially extending bearing surfaces concentric with the axis of rotation of said drum, said rings being constructed and arranged and so secured to said closure member and hopper that one of the joints between said rings is exposed to the outside of said closure and hopper and the other of said joints is exposed to the interior of said hopper, said joint exposed to the interior of said hopper comprising means defining a narrow gap filled with grease and opening from the inner wall of said hopper.

7. In a concrete mixer having a rotatable mixing drum provided with an opening through which material is charged into and discharged from said drum, an annular closure engageable with said drum for sealing said opening and being rotatable with said drum when so engaged, said closure being movable away from said drum so as to permit the discharge of material therefrom through said opening, a, material receiving hopper on which said closure is rotatably mounted and adapted to charge material through said opening in said closure and into said drum through the opening thereof when said closure is sealing said opening, means supporting said closure and hopper for movement away from and toward said drum, and means providing a bearing between said closure and hopper to permit relative rotation therebetween when said closure is rotating with said drum, said bearing means including a ring journalled on said hopper and forming a joint therewith remote from the discharge end of said hopper and on the inner wall of said hopper.

8. Apparatus according to claim 7 wherein said hopper is provided with a lip overhanging said joint.

9. Apparatus according to claim 7 wherein said ring is channel-shaped.

10. Apparatus according to claim 7 wherein said ring is channel-shaped and wherein the bearing surfaces between said hopper and ring are disposed within said channel-shaped ring.

11. In a concrete mixer having a rotatable mixing drum provided with an opening through which material is charged into and discharged from said drum, a closure engageable with said drum for sealing said opening and being rotatable with said drum when so engaged, said closure being movable away from said drum so as to permit the discharge of material therefrom through said opening, a material receiving hopper provided with a chute extending through said closure and into said drum through said opening when said closure is sealing said opening, said chute being carried by said closure and extending into said drum a substantial distance so as to charge material fed into said hopper into said drum at a distance inwardly away from said opening in said drum, means supporting said closure and hopper for movement away from and toward said drum, and means providing a bearing between said closure and hopper to permit relative rotation therebetween when said closure is rotating with said drum, said bearing means comprising a ring fixed to said closure member for rotation therewith, a ring fixed to said hop-per, said rings having interengageable annular axially extending bearing surfaces concentric with the axis of rotation of said drum, said rings being constructed and arranged and so secured to said closure member and hopper that one of the joints between said rings is exposed to the outside of said closure and hopper and the other of said joints is exposed to the interior of said hopper, said rings being constructed to provide a labyrinth efiect between said other of said joints and said bearing surfaces and a grease channel adjacent to said bearing surfaces.

12. In a concrete mixer having a rotatable mixing drum provided with an opening through which material is charged into and discharged from said drum, an annular closure engageable with said drum for sealing said opening and being rotatable with said drum when so engaged, said closure being movable away from said drum so as to permit the discharge of material therefrom through said opening, a material receiving hopper on which said closure is rotatably mounted and adapted to charge material through the opening in said closure and into said drum through the opening thereof when said closure is sealing said opening. means supporting said closure and hopper for movement away from and toward said drum, and means providing a bearing between said closure and hopper to permit relative rotation therebetween when said closure is rotating with said drum, said bearing means including a ring journalled on said hopper and forming a joint therewith remote from the discharge end of said hopper and onthe inner Wall of said hopper, said bearing means having a, joint exposed to the outside of said hopper and closure.

13. A concrete mixer having a charging hopper with a closure member rotatably carried by said hopper and a bearing between said closure and hopper, said bearing comprising a ringv fixed to said closure for rotation therewith, a ring fixed to said hopper, said rings having interengageable cylindrical bearing surfaces and thrust bearing surfaces disposed transversely to said cylindrical bearing surfaces, said rings being constructed and arranged and s0 secured to said closure and hopper that one of the joints between said rings is exposed to the outside of said closure and hopper and the other of said joints is on the inner wall of said hopper,

14. A concrete mixer according to claim 13 wherein said rings are constructed to provide a labyrinth efiect between said other joint and said bearing surfaces.

15. A concrete mixer according to claim 18 wherein one of said rings is channel-shaped in cross section and wherein the other of said rings is at least partially disposed in the recess provided by said channel-shaped section.

16. A concrete mixer according to claim 13 wherein each of said rings is secured to a sealing ring and wherein said sealing rings form a part of said hopper and are arranged in nesting relation with a narrow gap between adjacent portions thereof, said gap forming said other joint, one of said sealing rings being secured to said closure for rotation therewith and the other of said sealing rings being secured to said hopper.

17. A concrete mixer according to claim 13 wherein one of said rings comprises two separable parts secured together and defining an annular channel therebetween and wherein the other of said rings is provided with a portion running in said channel, said portion and said channel providing said thrust bearing surfaces.

18. A concrete mixer according to claim 13 wherein said closure member is secured to one of said rings and is provided with a portion arranged in overlapping relation with the other of said rings so as to secure said rings in assembled relation.

CHRIS GERST.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 615,519 Barr Dec. 6, 1898 2,454,940 Peters Nov. 30, 1948 2,489,885 Henderson Nov. 29, 1949 2,504,223 Pasquariello Apr. 18, 1950 2,544,083 Hawkins Mar. 6, 1951 2,544,545 Rockburg Mar. 6, 1951 2,545,485 Meisenburg Mar. 20, 1951 2,563,770 Yantes et a1 Aug. 7, 1951 2,567,729 Rockburg et a1. Sept. 11, 1951 

